Ingot mold



E. MARBURG INGOT MOLD June 16, 1953 2 Sheets-Sheet l Filed Dec. 6, 1950 INVENTOR. Mal-burg Edgar H/s ATTOEWH June 16, 1953 E. MARBURG 2,641,807

INGOT MOLD Filed Dec. 6, 1950 2 Sheets-Sheet 2 Jig. 5.

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Patented June 16, 1 953 moor MOLD Edgar Marburg Pittsburgh, Pa., assignor to United States Steel Corp oration,; a corporation of. New Jersey A pplicationD ecembfer 6, 1950; Serial No; 199,384;

a laime 01. za-lss) l: Thisinvention relates tosingotv molds especially to-ingot molds. of the big-endadown. type:and isa continuation-impart. of: my. copending. application, SeriaLNo. 780,055, filed. October 15,- 1947,

nowsabandoned.v ItLisapreferabletouusebigeenddown molds if -possiblesinceit is much easier: to strip the: mold from the ingot andit isalso possible. to' cast.. the: ingot without using: hot tops which may not -be': necessary: for some; types of steel. Since. big-'end up. ingots must. project above the mold im ordento beremovable by a stripping crane; such. ingots must always be:hot topped; However, secondary pipe was frequently fOund imbig-end-doWn ingots; the type originally in-almost universal use and therefore big-end-up molds-were developed and came into increasing However; except fon steel quality; big-end-downmolds'are preferable to big-end up. molds fromevery viewpoint of: steel production; Thebig-end-up ingot molds are more expensive than the big-endedown molds and' have a: shorter life; The big-end-up" ingots have rounded bases .and cannot stand-' upright in the-soaking pit; They have agreater taperthan big-end -down ingots and are-therefore more-difiicut to'roll." Thebig end-up-moldshave also other disadvantagesin additionto those listed above so that it is-apparent thatthe quality advantage obtained bythe use of big-end-up molds-must be very important to offset the obvious disadvantages of this type ofmold; T-he quality-advantage of big-endup molds-results from thefactthat the ingots are narrowen at thebase than --atthe: top,

which aids progressive. solidification from bottom to top, thus-minimizing bridging, secondarypipe and axial porosity. Even inusing the-bigend upmold, however, severe axial' porosity often occurs-:imingots ofintermediate-sizes- (18- 'to 25 -wide particularly inalloy steels; Center.- segregation (V -segregation) often-'- occursin ingots of intermediate size while outer rings of segregation of handling and rolling the ingots; Segregation a defects are--causedjby=the slow cooling of; ingots castirrccnventional molds; Ifthe-cooling-of the ingots can'be speeded up manyof the defectsmay beminimized or eliminated;

Toincrease the freezing rate or ingots it has a 5 Thiswould reduce the.

been; customary: to: increasethethickness; :of the mold wall. Besides increasing the cost andreducingthevlife of molds increasing the wall thicknessabove about 6!" for intermediate sizes. and 8" for large moldshas other disadvantagesas follows: The thick-walled molds contain more heat and must either be held out longer between use, or-thevwill be so .hotgwhen returned for. re-

use asto make difficult theaplacing. of: hotytops thereon. Increasing the:.wall; thickness. has the effect of: decreasing the. occurrence of inverted V-segregation-v in. ingots; but; of increasing the extent and intensity Orv-segregation.

I have. found that: it? a; mold is madezwithyvalls having alternatethick andthin sections around its periphery, the. distance'from. center.- to center of the thinsectionslbeing. 1101351885. than 12" on the internal periphery,- thethicksections initially extract heat and therefore solidify the adjacent steel atsa moresrapid rate. thanrdothe thin:sections of the mold:wall. The thin sections, however; quicklyrheat to aa higher temperature than do the thick sectionsso that; after; a; periodof about fifteen. minutes; a: considerable difference of -temperature, or:temperature; gradient exists between the thin and:thick portions. ofrthe mold. Phus heat will flowthrough themold wall from the thin to the thick sections; accelerating, heat extraction of the former and. reducing that of the lattersections. Bythis means; heat: extraction adj acent to the thin-walled. portionszof the mold may be accelerated: in the latter stages" of solidification which is-thecritical time for development of V and invertedsegregation. Thus the amount of'V-segregation and axial porosity may be reduced in. all ingots; the. size of ingots free from V-segregation may-beincreased, while theoccurrence of inverted V'-segregati0n in ingots larger than this size may be: reduced: If themolds are square or rectangular the sides are preferably made-thin, so astobeat the closest distance to'thecenter of the ingot and the, corners are madethick. Inroundlingots', of: course, no suchpreferenceexistsand thiniand thick sections arealternated.

It is also-= desirableto have the freezing. rate progress a from thebottom to the top and. Iv have found that this canbe done by making theratio between the thickness: of the thick and thin sections greaterat the base-than at thetoplof-a big-end-down-mold.

It istherefore an object of my invention to provide" an ingot: moldwhich. causes ingots to freeze progressively-from the bottom to the top.

Another obj ect'is to provide a mold in. which 3 ingots having a minimum taper /2 per side) can be cast.

Still another object is to reduce the time of complete solidification f ingots of all sizes over 18 wide.

A further object is to reduce V-segregation, axial porosity, and inverted V-segregation in commercial ingots.

These and other objects will be more apparent after referring to the following specification and attached drawings, in which:

Figure 1 is a top view of the mold;

Figure 2 is a bottom view of the mold of Figure 1;

Figure 3 is a side view of the mold in Figures 1 and 2;

Figure 4 is a side view of the mold in Figures 1 and 2 taken at right angles to Figure 3;

Figure 5 is a top plan View of a second modification of my invention;

Figure 6 is a'bottom view of the mold of Figure 5;

Figure 7 is a side view of the mold of Figure 5;

Figure 8 is a sectional view taken on the line VIII-VIII of Figure 7; and

Figure 9 is a top plan view of a further modification of my invention.

The preferred embodiment of my invention is shown in Figures 1 to 4 with the thick sections being at the corners and the thin sections on the sides Of the mold. -As shown in Figure 1 the corner areas of the top portion of the ingot are indicated by the reference numeral 2 and extend between the dash-dot lines as indicated, while the side areas are indicated by the referenoe numeral 4. The corresponding corner and side areas at the bottom of the mold are indicated by the reference numerals 6 and 8, respectively.

It has been found that a convenient arrangement for varying the thickness of the Walls of the ingot mold is to use the standard corrugated internal periphery as shown, while making the outer periphery of each of the sides the arc of a circle having its center outside the mold approximately on a line extending from the center of the mold through the center of the side. The outer periphery of each corner is conveniently made as the arc of a circle having its center inside the mold on a line extending through the center of the corner of the mold at approximately 45 to the adjacent sides. This arrangement gives uniform transverse cooling of the ingot. The radii of the arcs of the circles at the corners and sides as described above are determined by the thicknesses of wall desired at the center of the sides and at the corners, and by ingot sectional dimensions, in accordance with design considerations described below.

In order to vary the freezing rates to cause faster freezing at the base than at the top of the ingot, the ratio between the thickness of the corners and sides is made greater at the base than at the top of the mold. This has been conveniently done by making the lower section 1" narrower than the top section in all vertical planes. Thus, for the mold shown, the thinnest thickness of the side at the top is 3% and at the base 2%. The thickest thickness of the corner at the top is 7%" and at the base 6%. Thus, the ratio of the thick corner to the thin side of the top is 2.1, while at the base the ratio is 2.5. Comparing the relative areas as indicated .in the drawings, we may assume the side area to comprise 40% of the overall width and on this basis the corner area 2 of the top is 1.37 times as great as the side area 4, while the corner area 6 of the bottom is 1.85 times as great as the side area 8. The corner-side ratio is therefore considerably greater at the bottom than at the top of the mold. With this arrangement of the mold the thickness of the side at the base is 1" narrower than the thickness Of the side at the top so that the side at the base will attain a higher temperature than the side at the top. Since there is less proportional difference in thickness between corners 2 and 6 than between sides 4 and 8, and since the corners are considerably lower in temperature than the sides, considerably less difference in temperatures will occur between corners 6 and 2 than between sides 8 and 4. As a result, there will be a considerably greater temperature differential between side 8 and corner 6 at the base than between side 4 and corner 2 at the top. As a result of this increased temperature differential and the increased corner side ratio at the bottom, heat will be extracted from the sides at a considerably faster rate toward the base of the ingot than at higher levels. Also, since the wall is thinnest at the base, the actual temperatures will be maximum at the base in all vertical planes so that any heat flow longitudinally through the mold wall must be upward from the base. Thus the increased rates of transverse solidification produced by the corner/side ratio being maximum at the base cannot be interfered with by opposing heat flow in the mold wall. The above analysis of heat fiow applies up to the time at which the base of the ingot becomes completely solid at which time less heat is available from the ingot interior. On account of the heat lost to the stool on which the mold rests, the base of the ingot solidifies fairly rapidly (approximately 12" high in 30 to 60 minutes, varying with the ingot size). When the temperature of the mold wall at the base drops as a result of reduced heat from the ingot, heat will fiow downwardly in the mold wall, reversing the previous direction of flow. However, this will merely accelerate solidification progressively upwardly because the mold temperatures at intermediate heights prior to complete solidification will always be higher than those above until the ingot is completely solid.

Experiments have shown that a mold wall of non-uniform sections as described above, not only extracts heat from the ingot at a faster rate than attainable by a uniform mold wall of thickness equal to the thinnest part of the sides, but does so in a desirable sequence, thus resulting in the maximum improvement in the soundness of the ingot. For example, the initial rate of heat extraction by the thin sides is at the low rate normally occurring with uniform walls of the same thickness as the thinnest part of the sides. As the thin side walls become hot ter, the temperature difference between them and the corners increases, resulting in increased heat flow from the sides to the corners. This rate increases until it is greatest when the mold temperature is highest. Since this requires an appreciable length of time (approximately 30 to 45 minutes), the ingot has frozen to a consider- I able depth before the maximum rate of heat ex- 1 traction is attained. It is at this depth that inverted V-segregation normally commences to develop, but the increased rate of solidification prevents its development so that the ingot is sound with minimum segregation. In molds of uniform wall: thickness. the. rates of-iheatiextractioni is: at aminimum whenthe mold temperaturezisgreate est, becauseat this; time 1 therezis :the least; difference. intemperature between; the ingot; and mold; This is the-most: favorable condition; for causing V-segreg'ation inthe ingot;

The mold of non-uniform wall thickness has thus beenfound capable of extracting heat in the critical later stagesof ingot solidification at faster ratesthan are possible in uniform molds of y racticable-wallthickness.

While Figures 1 to 4 show apreferred embodiment of my, mold it is only necessarythatthe mold be provided with alternate thick. andithin sections around its periphery with the distance from center to center.-of=the=thinsections being not less-than 12 on theinternal periphery ofthe mold. If this distance isanyless, the essential temperature gradients will not develop. The ratio between the thickness of the thick and thin sections at the top compared to the thickness of the thick and thin sections at the bottom ofthe mold may also be increased by increasing the thickness of the corners (or thick portions) at the base while maintaining the sides (or thin portions) of the same thickness from top to bottom. Another method of varying the ratio is to maintain the same thickness of the corners and the middle of the sides vertically while reducing the diameter of the circular are at the base and tapering it upwardly and outwardly toward the top. Still another method of varying the ratio is to decrease the thickness of the sides at the base relative to the top while maintaining the corners the same thickness throughout the height.

Another modification of my invention particularly adapted for large rectangular molds for slabbing ingots is shown in Figures 5 and 6. In these large rectangular molds (for example, 24" x 48" ingot molds), completion of the freezing of the ingot always occurs across the narrow dimension. In order to accelerate this rate of freezing, the-long sides I0 are made thinner, and the ends of these long sides made thicker and/or the corners and/or the ends of the short sides l2 made thicker. As shown, the sides It) .are reduced in thickness by providing a centrally located recess H! in the outside surface thereof. As best shown in Figures 7 and 8, this recess increases in width, but decreases in depth from the bottom upwardly until it just disappears at the top of the mold.

Increase of thickness of the side walls toward their ends for the purpose of accelerating transverse solidification across the narrow central vertical plane may also be obtained by reducing the width of the ingot toward its ends, as shown in Figure 9. In this embodiment the long sides [6 of the mold are gradually increased in width at their ends by providing a tapered inner wall l8. This method of increasing the thickness of the side walls is principally applicable to large rectangular slabbing molds, because if applied to square molds, their interiors would approach an octagonal shape. The cross-sectional shape of the ingot cast in this mold is a desirable one for rolling as it tends to prevent corner cracks which frequently develop in the initial passes in rolling. The relative thicknesses of the sides and ends of the mold at the top and bottom may be designed to insure more rapid solidification at the bottom and to prevent heat flow in the Y '6 many-instances; this:-.variation:-.in relativeathicke nessof the sides-and ends is notxnecessary: in large rectangular molds- While various. embodiments; of! my invention have been showniand described; it; wilLbeapparent that other; adaptations. and modifications may-:be. made without: departing from. the scope of-the following. claims.

Iclaimz- 1; A: rectangular ingot: mold; having-relatively thin side. walls. and; relatively. thick. end walls and: corners throughout: the height;;of1- the: mold, the: distance frorns center to center; of: the: thin sides: on the internal peripheryr being at least twelve inches, the ratio between the thicknessmf the: end and side walls :decreasing from. the base to=the top of the mold.

2. A rectangular ingot moldaccording to claim 1- inwhich thethickness. of: the sidewalls; is reduced at the center thereof.

3. An ingot mold of generally polygonal form in cross-section having side walls and corners with at least two of the side walls being of less thickness than the adjacent corners throughout the height of the mold, the distance from center to center of the thin sides being at least twelve inches on the internal periphery, the thickness of the walls increasing from the bottom to the top thereof.

4. An ingot mold of generally polygonal form in cross-section having side walls and corners with at least two of the side walls being of less thickness than the adjacent corners throughout the height of the mold, the distance from center to center of the thin sides being at least twelve inches on the internal periphery, the ratio between the thickness of the corners and sides decreasing from the base to the top of the mold.

5. An ingot mold of generally polygonal form in cross-section having side walls and corners with the side walls being of less thickness than the adjacent corners throughout the height of the mold, the distance from center to center of the thin sides being at least twelve inches on the internal periphery, the outer periphery of each of the sides being the arc of a circle having its center outside the mold approximately on a line extending from the center of the mold through the center of the side, and the outer periphery of each corner being the arc of a circle having its center inside the mold approximately on a line extending from the center of the mold through the center of the corner, the thickness of the walls increasing from the bottom to the top thereof.

6 An, ingot mold of generally polygonal form in cross-section having side walls and corners with the side walls being of less thickness than the adjacent corners throughout the height of the mold, the distance from center to center of the thin sides being at least twelve inches on the internal periphery, the outer periphery of each of the sides being the arc of a circle having its center outside the mold approximately on a line extending from the center of the mold through the center of the side, and the outer periphery of each corner being the arc of a circle having its center insid the mold approximately on a line extending from the center of the mold through the center of the corner, the ratio between the thickness of the corners and sides decreasing from the base to the top of the mold.

7. A rectangular ingot mold having relatively thin side walls and relatively thick end walls and corners, the thickness of the side Walls being reduced at the center thereof, the distance from center to center of the reduced portions of the side walls being at least twelve inches on the internal periphery, the thickness 'of the reduced portion of the side walls being greater at the top than at the bottom of the mold.

8. A rectangular ingot mold having relatively thin side walls and relatively thick end walls and corners throughout the height of th mold, the distance from center to center of the thin sides on the internal periphery being at least twelve inches, the ratio between the areas of the thick sections and the areas of the thin sections decreasing from the base to the top of the mold.

9. An ingot mold of generally polygonal form in cross-section having side walls and corners with at least two of the side walls being of less thickness than the adjacent corners throughout EDGAR MARBURG.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,758,823 Blage May 13, 1930 1,792,581 Firth Feb. 17, 1931 FOREIGN PATENTS Number Country Date Germany June 25, 1917 

